1. Field of the Invention
The present invention relates to semiconductor substrate processing equipment. More particularly, the present invention relates to a method and apparatus for reducing undesirable deposition of material on the backside of the substrate during processing. Still further, the invention relates to method and apparatus for supporting a substrate in a processing chamber.
2. Background of the Related Art
The fabrication of semiconductor devices on substrates, including semiconductor substrates, typically requires the deposition of multiple metal, dielectric and semiconductor films on the surface of the substrate. The films are typically deposited on the substrates in vacuum chambers. One deposition technique is physical vapor deposition (PVD) typically referred to as sputtering, wherein a target comprised of the deposition material is exposed to a plasma and atoms or larger particles of target material are sputtered from the target and are deposited on the substrate.
To form the deposition layer on the substrate, a deposition environment must be created within the chamber adjacent to the deposition receiving surface of the substrate. In a physical vapor deposition system, the deposition environment includes a plasma maintained between the target and the substrate and a flux of sputtered target particles passes between the target and the deposition receiving surface of the substrate so that a portion of the sputtered target particles deposit on the substrate to create the deposition layer.
FIG. 1 is a simplified sectional view of a conventional PVD chamber 10 which generally includes a chamber enclosure wall 14 having at least one gas inlet (not shown) and an exhaust outlet 16 connected to an exhaust pump (not shown). A substrate support member 20 is disposed at the lower end of the chamber 10 and a target 18 is received at the upper end of the chamber 10. In addition to providing a resting and lifting mechanism, the support member is also used to dissipate the heat generated during deposition. The target 18 is electrically isolated from the enclosure wall 14 and the enclosure wall 14 is preferably grounded so that a negative voltage may be maintained on the target 18 with respect to the grounded enclosure wall 14. A shield 22 is suspended from the chamber cover and includes an annular, upturned, wall 24 which isolates the lower portion of the chamber when the substrate support member is in a raised position for processing
A conventional robot arm carries a substrate 26 into the chamber 10 and positions the substrate 26 above the upper tips of the pins 30a. A lift mechanism 32 elevates platform 28 which lifts the pins 30a upwardly to lift the substrate 26 off the robot blade. The robot blade then retracts from the chamber 10, and a substrate support lift mechanism 60 raises the support member 20 and the lift pins are lowered to place the substrate 26 on a resting mechanism coupled to the support member.
The resting mechanisms generally provided in conventional processing chambers are prone to producing contaminants by scratching the backside of the substrate. During the deposition process, the substrate is disposed on one or more rest pins 88. The rest pin 88 is rigidly fastened to the support member 20. Thus, vibrations in the support member are communicated to the support pins which results in friction between the support pins and the backside of the substrate. Friction between the support pins and the substrate may lead to deep scratches in the backside of the substrate, thus releasing substrate material which contaminates the environment within the chamber.
In physical vapor deposition systems, the deposition material will, if left unconfined, deposit on all of the interior surfaces of the chamber. Typically, material is sputtered in a cosine pattern. In particular, material which does not deposit on the material receiving surface of a substrate may deposit on the edge or backside of the substrate. Edge and/or backside deposition may lead to damage of the substrate and adhesion or sticking of the substrate to components of the processing chamber. In particular, backside deposition may lead to the formation of bridging layers between the backside and the support member in the chamber leading to adhesion of the substrate to the support member. Adhesion of the substrate to the support member is generally referred to as sticking.
In conventional chambers used for full coverage deposition on substrates, a large gap must be maintained between the support member and the substrate to delay the formation of a bridging layer between the substrate and the support member due to the accumulation of material in the space between the backside of the substrate and the support member. However, maintaining a large gap between the support member and the substrate may drastically reduce the efficiency of heat dissipation by the support member.
In spite of the space maintained between the support member and the substrate, deposition in the area of contact between the resting and lifting mechanism and the substrate generally results in accumulation of material capable of adhering to the substrate and the support member, thus necessitating operator intervention to separate the substrate from the resting mechanism which leads to substantial down time of the chamber.
One avenue for reducing edge and backside deposition and the related adhesion and contamination problems is provided by forming a rectangular channel in the periphery of the support member. Material which deposits at the perimeter of the substrate is collected in the channel and prevented from accumulating at the edge of the substrate and ultimately forming a bridging layer between the support member and the backside of the substrate.
FIG. 2 is a partial sectional view of a substrate support member having a rectangular collection channel 96 for material collection and a substrate support pin 88 disposed in the support member to support the substrate 82. The upper surface 84 of the substrate 82 is exposed to a target (not shown) and the backside 86 of the substrate contacts support pin 88. The support member 90 has a substrate receiving region 92 and a peripheral region 94 comprising a collection channel 96 disposed therein. The collection channel 96 is formed by sidewalls 102, 104 and a base 106. The edge 108 of the substrate 82 extends beyond the substrate receiving region 92 and over hangs the collection channel 96 when supported in the chamber. During processing, material deposits on the entire surface of the material receiving face and in the collection channel 96. As the deposition material impacts the walls of the collection channel 96, the material may lose kinetic energy during the impact and accumulate in the collection channel 96. The top end of each wall 102, 104 may be machined to include chamfers 112, 114 that may contact particles from the depositing material and divert their trajectories to avoid contact between the material and the backside 86 of the substrate 82.
Although the design of FIG. 2 may allow material deposition over the full surface of the material receiving face 84 while accumulating in the collection channel 96, the design may only marginally decrease backside deposition. After impacting the walls 102, 104 and/or the base 106, only particles with low kinetic energy will likely remain within the collection channel 96 while other particles contacting the walls and the base of the channel will have enough kinetic energy to continue their trajectory, have a number of impacts with the walls and the base of the channel, and possibly continue on a trajectory 101 which guides them to the backside 86 of the substrate. While the chamfers 112, 114 may deflect some of the particles away from the backside of the substrate, other particles may impact the chamfers at angles that would actually direct their trajectories 103 towards the backside of the substrate, and some particles may even end up near the contact region 89 between the support pin 88 and the substrate resulting in adhesion of the substrate to the support pin. The deposition of particles near the contact region 89 and the deposition of material bridging the backside of the substrate and the support pin are enhanced when the outer surface of the support pin has a steep slope to form a large gap 87 between the top portion of the support pin 88 and the backside of the substrate near the contact region 89.
Another problem encountered with the support pins 88 is backside scratching of the substrate. The support pins 88 are rigidly fixed to the support member 90 thereby translating the vibrations of the system to the backside of the substrate near the region 89. Increased relative movement between the support pins 88 and the substrate increases the likelihood that scratching on the backside of the substrate occurs thereby increasing the potential for contamination in the chamber. Furthermore, the problems relating to the friction between the substrate and the equipment are generally complicated when the deposit material reaches the backside of the substrate, particularly near the area of contact between the resting mechanism and the backside of the substrate.
The limited reduction in backside deposition and substrate sticking provided by the design of FIG. 2 requires maintaining a gap of at least 40 mils between the substrate and the support member to delay the formation of a bridging layer between the substrate and the support member. Typically, maintaining a large gap between the substrate and the support member is achieved by reducing the thickness of the support member, thus reducing the capacity of the support member to dissipate the heat generated during substrate processing.
Therefore, there is a need for a method and apparatus that would allow full coverage substrate processing and efficient heat dissipation during substrate processing while reducing material deposition on the backside of the substrate by trapping a substantial fraction of the deposition material in a collection channel. Additionally, there is a need for methods and apparatus which reduce or eliminate substrate scratching and the contamination which results therefrom.